Adjusting trim

[ppriest]

Waking to some unexpectedly pleasant conditions on the
Strait this morning Verla and I took the J.C.Lately out for a turn around Protection Island to look at seabirds, circulate motor oil, and play with some of the recionfigurations on the C-80 plotter. Recalling some recent posts which dealt with, among other things, fore and aft trim on CD-22s I realized that at the end of our first seaon's operations we still don't have a well-defined procedure for properly trimming the boat fore and aft.
We trim laterally using the forward edge of the cuddy hatch as a reference and deploying the hydraulic trim tabs differentialy to make the edge parallel to the horizon.
We've been adjusting motor trim to position the same edge some arbitraty distance below the horizon; but I realised that this operation has little to do with actually achieving the optimal horizontal fore and aft trim of the boat.
Looking at the vessel on the trailer this afternoon I noticed that the plane of the cuddy hatch appears to more or less parallel the waterline applied to the boat, but if that is actually a good indicator of fore and aft trim when the boat is on plane, then we are still far from having the vessel properly trimmed.
Suggestions for a procedure?

Paul Priest
Sequim

[Plan C]

I have done two things to figure correct trim. One was to travel next to another C-Dory at cruise speed, and notice when it was properly trimmed where the bow wave appeared, relative to helm window. About even looked right.

And then the ultimate test is merely to watch your GPS speed over ground, and experiment with trim until you find for the same throttle setting where the fastest speed is. Turns out to be about same as Number One.

Dave

[C-Green]

I use method number 2 all the time. First I do a lateral trim using an RV bubble level I installed at the helm. Then I trim the motors to level by eye. Then I go back and forth between adjusting the trim tabs (equally at the same time) and the motor trim; always leaving the throttle alone and adjusting whichever trim for maximum speed. After two or three rounds of adjustment I'm at max speed. I feel this gives me max fuel economy, a good thing.

[thataway]

I would agree that in flat water, the best trim of the boat is to try and find the most effecient attitude by speed and throttle setting. When you have trim tabs and motor trim, there are two variables.

Often we set the trim tabs to give the best ride for the surface conditions, and then bring the engine trim so that the prop thrust is most effecient (usually fairly close to horizonatal and parallel to the water surface.) When you have a fuel flow meter, this adds even another perimeter to the "most effecient"--but the keeping the throttle setting constant and using the trim to give the best speed works well for the best effeciency.
With Permatrims, the trim effect of the motor is accentuated.

Sometimes when the water is rough, it is best to trim for the best ride--rather than the best effeciency--even though it uses more fuel. This may be with the bow down in some conditions. So there is no one answer, but it varies with sea conditions, direction of travel in reference to the waves etc.

Another way to look for "trim" is to put inclinometers reading to five or ten degrees (you don't need the instrument which reads to 45 degrees) so you can see if the boat is "level" both fore and aft and athwartships. I sent the inclinometers "level" to the boat's cabin floor as a reference. Inclinometers are used in sailboats to determine the degree of heel--but also used on power boats to see that the boat is level fore and aft, and side to side. If the boat is "level" from side to side, fuel effeciency also improves, and that is where the inclinometer is helpful. The inclinometers allow you to be consistant in trim.

However, when in rough weather, I am often working the trim as well as throttles and steering, depending on the sea conditions. For example when you are running down waves, and encounter a larger wave, you may want to trim the bow up, even though for the average seas the boat
is trimmed properly. These principles work in most boats, including the cats, but the actual amount of trim is different in each type boat.

[Doryman]

Further to this discussion about trim -- Bob, and other TC owners -- have you noticed that when you trim one of the motors the trim of the other motor is affected? I am talking about the display on my Yamaha Command Link displays, but I imagine that Honda and Suzuki have similar displays showing the amount of trim dialed in. Do you have a technique for dealing with this or do you ignore the display?

Warren

P.S on edit -- I am referring to port/starboard trim.

[Hunkydory]

Use trim method very similar to Bob's. Adjust the motor trim so props are as horizontal as possible with boat on trailer, then marked spot on motor trim gauges, so can return there when needed. Then on the water adjust boat trim tabs to give best speed on gps. Also quite happily give up fuel economy for smooth ride in chop by further adjusting trim tabs to lower the bow even more.

I have experimented a lot with this and found the end results were best if I started with moter trim and props horizontal then to trim tabs for best speed at a given rpm.

Jay

[drjohn71a]

Warren,

I have noticed that the little hash marks have an "on the fence" position wherein the slightest change in the boat's attitude will make the next hash mark appear or disappear. Then there is a wider zone of movement in which the hash mark stays the same while the trim changes. When yours does that, just bump the switch a bit to make it match the other engine and I think that will 'knock it off the fence' so to speak.

John

[ppriest]

Thanks, All, for your responses and suggestions - we'll give them a try.

I'm still trying to assemble a set of procedures and numbers analogous to the number set I acquired and used satisfactorily for 750 hours of flying in light airplanes. Things are beginning to gel although in the absence of a personal mentor, it's a little slower going. Thanks again.

Paul

P.S.: Bob, I sent a couple of PMs with questions regarding sea conditions. Have they gone adrift or just not made it to the top of your list yet?

[thataway]

Ppriest, the PM must have been lost in cyber space. It is strange, I was looking at my "out" box recently, and there were a number of messages there, which meant that they were never picked up by the recepients.

If this is the case, then please feel free to send an E mail.

On the Cats--and trim. Most dual installations of outboards, allow you to trim single motors, or dual motors, with either one of the trim tabs. Again, I don't trim entirely by looking at the guage, but how the boat is running, fuel flow meters, speed, throttle settings etc. What I do notice is that there is some "drift" in the "synchronization" of the motors, so that occasionally, I will put both motors down, and start from that point so that they are together and at the same degree of trim.